1. Field of the Invention
The preset invention relates to a servo controller having a function for reducing an amount of dropping of a gravity axis when braking the gravity axis.
2. Description of the Related Art
In a configuration wherein a feed axis, etc., of a machine tool or an industrial machine is driven, in case that an axis driven by a servomotor is subject to external force, in particular gravity force (hereinafter, such an axis is referred to as a “gravity axis”), the gravity axis may fall by gravity when power to the servomotor is shut and the gravity axis is in the uncontrolled state.
As a technique regarding the dropping of a gravity axis, for example, JP 2003-131701 A discloses a controller for a servomotor. The controller is configured to output a command for lifting a gravity axis of a machine driven by a servomotor by a predetermined distance, and output a command for braking the gravity axis by means of a brake device, when the machine is in an emergency stop state or a power outage state.
Further, JP 2010-215369 A discloses a servo control system used in a turning operation machine such as a crane car, wherein a load axis is driven by an electric motor via a plurality of gears. In order to reduce an influence due to a backlash between the gears, the servo control system is configured to limit output torque of the motor during the passage of a predetermined period of time corresponding to time required for movement of one gear by a backlash width, when the motor is reversed or decelerated.
In JP 2003-131701 A, it is described that the object of the invention in this document is to prevent dropping or falling of the gravity axis when the gravity axis is braked. However, in JP 2003-131701 A, when a means for stopping the gravity axis during the braking should be switched from motor control to a mechanical brake, the gravity axis is previously lifted by a distance larger than the amount of dropping before the mechanical brake is activated. Therefore, in JP 2003-131701 A, the amount of dropping of the gravity axis is not decreased.
On the other hand, the object of the invention in JP 2010-215369 A is to prevent vibration, noise and decrease in a machine life due to the backlash, and is not to reduce the amount of dropping of the gravity axis. Further, in JP 2010-215369 A, it is described that the output torque of the motor is limited during the passage of the predetermined period of time corresponding to time required for movement of the second gear by the backlash width. However, this document does not concretely describe as to what value the torque is limited to.